#include<iostream>
#include<cmath>
#include<iomanip>
using namespace std;
int main()
{
	double x1, y1;
	double x2, y2;
	double length;
	cin >> x1 >> y1;
	cin >> x2 >> y2;
	cout <<fixed<<setprecision(3)<< sqrt(((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)));
	return 0;
}